This invention relates to methods and systems for manufacturing air bag cover assemblies and, more particularly, to methods and systems for manufacturing air bag cover assemblies including switches utilizing infrared radiation.
When one wishes to attach plastic parts together, several processes exist to accomplish this. Among them are methods such as hot air bonding, sonic welding, vibration welding, adhesives, mechanical fasteners and infrared radiant heat.
U.S. Pat. No. 5,750,970 discloses a method of dielectrically heating an adhesive which, in turn, bonds plastic parts together.
Infrared radiant heat has certain advantages over the other types of processes. Generally, there is a desire to form a strong bond between the two parts quickly at a minimal cost. Additionally, it is preferable that during the bonding process nothing touches the surfaces to be bonded in order to assure uniform bonds from part-to-part and to reduce the cost of cleaning the bonding apparatus. Further, in many instances, it is preferable that no marring or distortion occur on the surface opposite the surface which is bonded. This surface is referred to as the xe2x80x9cviewingxe2x80x9d or xe2x80x9cclass Axe2x80x9d surface.
Infrared bonding, in general, can overcome many of these concerns. Infrared energy can be finitely pinpointed with a focal point or a mask to the exact area to be bonded in order to avoid overheating the plastic in adjacent areas that might cause unwanted distortion in the part. Infrared energy can heat the bonding surface to a high temperature, thus assuring that a strong bond is formed between the two parts. The bonding surface can be heated very quickly with infrared energy and the timing and amount of heat application can be precisely controlled. Further, with infrared heating, there need be no contact between the heat source and the bonding surfaces of the parts, in order to minimize cleaning requirements for the tooling.
Nonetheless, there are some drawbacks, in general, to using infrared heat to bond plastic parts together. In the case of automotive interior parts, for example, there are many parts made of plastic that are bonded to another part, but also need to have their viewing surfaces as distortion and mar free as possible since occupants of the vehicle will be able to see the surfaces. However, in the general application of focused infrared heat on the bonding surface in such applications, the xe2x80x9cclass Axe2x80x9d surface is oftentimes damaged. The finite focal point, while avoiding overheating adjacent areas, is too intense and harms many plastic parts during the heating process. An inherent difficulty to overcome in working with infrared radiant heat to bond plastic is to heat the bonding surfaces sufficiently without causing warpage, burning or marring of the xe2x80x9cclass Axe2x80x9d surfaces.
U.S. Pat. Nos. 3,383,265; 3,549,451; 4,265,954; 5,151,149; 5,244,525; 5,444,814 and 5,522,954 all disclose the use of infrared energy to bond or join plastic or polymeric materials together. The ""954 patent discloses the bonding of plastic interior automatic parts having xe2x80x9cclass Axe2x80x9d surfaces after each surface is exposed to infrared heat from an infrared heat source positioned between the surfaces.
U.S. Pat. No. 4,096,306 discloses a method of forming air-inflated cushioning material using two heat sealable films with air passages therebetween, which may be fused by xe2x80x9cinfrared black line sealing.xe2x80x9d
U.S. Pat. Nos. 5,062,661; 5,487,557; 5,465,998; 5,549,323; 5,558,364; 5,520,412; 5,542,694; 5,399,819; and 5,522,954 disclose a variety of heat-staking and hot plate welding techniques with respect to automotive air bag covers.
Securing back plates to front panels of plastic air bag covers present unique problems especially since the space between the front panel and the back plate defines a critical gap in which a membrane switch is positioned prior to the staking process. The size of the gap is critical to ensure proper switch actuation, which most often takes the form of a horn actuation. Furthermore, the back plate must be secured to the front panel so that the back plate does not separate from the front panel during air bag deployment within an automotive interior temperature range of xe2x88x9230xc2x0 C. to 80xc2x0 C.
U.S. Pat. No. 5,685,561 discloses the induction welding of a back plate to the back side of an air bag cover.
U.S. Pat. No. 5,642,901 discloses a relatively flexible thermoplastic air bag cover including a front panel wherein switch-activating members enhance activation of a membrane-type switch located at a switch location area of the front panel.
One prior art staking process used hot air to melt rearwardly extending stakes from the front panel onto the back plate. However, the hot air also tends to: 1) deform the xe2x80x9cclass Axe2x80x9d surface of the front panel; 2) deform the switch membrane due to the hot air flow into the critical gap; and 3) deform the back plate, thereby changing the dimensions of the critical gap.
The use of heat-activated adhesive to bond parts together is shown by the following U.S. Pat. Nos. 5,228,108; 5,743,982; 5,486,252; 5,858,159; and 5,743,408.
An object of the present invention is to provide a method and system for manufacturing an air bag cover assembly including a switch quickly and inexpensively without introducing deformities into the resulting assembly.
Another object of the present invention is to provide a method and system for manufacturing an air bag cover assembly including a switch using infrared radiation.
Yet another object of the present invention is to provide a method and system for manufacturing an air bag cover assembly including a switch without introducing deformities into the outer xe2x80x9cclass Axe2x80x9d surface of a front panel, the switch, or a back plate while at the same time, ensuring that the back plate remains attached to the front panel during air bag deployment, (i.e. temperature range of xe2x88x9230xc2x0 C. to 80xc2x0 C.).
In carrying out the above objects and other objects of the present invention, a method of manufacturing an air bag cover assembly is provided. The method includes providing a front panel, a back plate, a switch and infrared-absorbing material. The method also includes positioning the front panel and the back plate so that inner surfaces of the front panel and the back plate define a switch pocket therebetween. Then the method includes positioning the switch in the switch pocket. The method further includes directing infrared radiation at the infrared-absorbing material for a time sufficient to heat the infrared-absorbing material to a desired temperature. The method includes controlling the amount of heat applied to the infrared-absorbing material by the infrared radiation and cooling the heated infrared-absorbing material. The cooled material fixedly secures the back plate to the front panel.
Preferably, the method further includes the step of forcing the heated infrared-absorbing material to flow prior to the step of cooling.
Still further in carrying out the above objects and other objects of the present invention, a system is provided for manufacturing an air bag cover assembly including a front panel, a back plate, a switch and infrared-absorbing material. The system includes an infrared lamp for emitting infrared radiation and a base having a fixture mounted thereon for receiving and retaining the front panel and the back plate so that inner surfaces of the front panel and the back plate define a switch pocket therebetween. The system further includes a controller coupled to the infrared lamp for controlling power supplied to the infrared lamp so that the infrared lamp emits infrared radiation at the infrared-absorbing material for a time sufficient to heat the infrared-absorbing material to a desired temperature. The heated infrared-absorbing material bonds the plastic parts together when cooled.
The system may include a mechanism mounted for movement relative to the base for forcing the heated infrared-absorbing material to flow.
In one embodiment, the back plate includes a plurality of spaced holes extending therethrough and the infrared-absorbing material forms a plurality of stakes connected to the inner surface of the front panel and extending through the plurality of spaced holes. The heated infrared-absorbing material forms a plurality of solid connectors when cooled.
In another embodiment, the infrared-absorbing material is a heat-activated adhesive and the method further includes applying the adhesive to at least one of the inner surfaces.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.